Electromagnetic Induction

What is electromagnetic induction?

It is the production of an emf by a changing magnetic field.

Faradays Law of electromagnetic inductionThe induced emf in a conductor is directly proportional to the rate of change of magnetic flux through the conductor.

This is the principle behind the electric generator or dynamo.

What is magnetic flux?

Magnetic flux φ = B X A

The unit of magnetic flux is the weber.

To demonstrate electromagnetic induction (or Faradays Law)

Mutual Induction

Mutual induction occur when the changing magnetic field surrounding one coil causes an emf to be induced in a nearby coil.

The transformer is a practical application of this principle

Step downtransformer

The Transformer Equation

OUT

IN

S

P

V

V

N

N

NP = Number of turns in the primaryNs = Number of turns in the secondaryVin = Voltage inVout = Voltage out

Energy Losses in the transformer

Ideally

Power in = Power out

(VI)IN=(VI)OUT

Energy Losses in the transformer

To reduce energy losses.• Laminate the core-this reduces currents

induced in the core• The low voltage coil carries the greatest

current so it should be made of thick wire which has low resistance.

• The core is made of iron which is easy to magnetise and demagnetise.

Self Induction

The production of an emf in a coil due to its own changing magnetic field.To demonstrate self inductionThe neon lamp flashes when the switch is opened as the rapidly collapsing magnetic field induces a large emf in the coil. (self induction)

Alternating Current

This trace may be shown using an oscilloscope.

RMS Values of AC

20II rms

20VVrms

When calculating power with AC always use the rms values not the peak values.

AC and CapacitorsA charged capacitor blocks DC but conducts AC.

AC and inductorsInductors and AC

Inductors act as resistors to AC.If the power source is DC the current through a coil is greater than if the

power source is AC. This is due to the induced emf that opposes the applied emf.

Uses of inductors1.Dimming stage lighting2.Tuning radios